1. Field of the Invention
The present invention relates to immersible heaters and more particularly pertains to an immersible heater for use in a diesel fuel tank which includes a pair a concentrically aligned tubular members having a cylindrical space defined therebetween so as to provide for efficient heat circulation within the diesel fuel tank.
2. Description of the Prior Art
With respect to the development of immersible heaters, it has been the general practice to utilize only a single tubular member which is insertable in a fluid, such tubular member having a heating element positioned therein whereby heat accumulating inside the tubular member may be conducted through the walls thereof into the surrounding fluid to heat the same.
In this respect, U.S. Pat. No. 1,723,743, issued Aug. 6, 1929, to Mason, is illustrative of the state of the art with regard to prior art immersible heaters. The Mason heater consists of a single tubular member which is fluid-tight and which is insertable into a tank containing a fluid so that the fluid is in contact with an outer surface of the tubular member. A light bulb is then suspended on an electric cord down into the tubular member so as to heat the air therein, such heat being conducted through the walls of the tubular member into the surrounding fluid. This construction presents a number of problems in that the light bulb may be easily broken during insertion or removal from the tubular member since no rigid structure is provided to control the movement of the light bulb within the tubular member. In other words, the light bulb is free to swing back and forth upon the electrical cord from which it is suspended, and since the Mason device utilizes AC current, there is an extreme danger of electrical shock involved. Further, the tubular member of Mason must necessarily be of a large diameter so as to provide sufficient space for the insertion or removal of the light bulb serving as the heating element. As such, a large volume of air is present within the tubular member and a large loss of efficiency results since much of the provided heat will never be directed into direct contact with the inner surface walls of the tubular member so as to be conductibly transferred into the surrounding fluid. In other words, only that portion of heated air coming into direct contact with the inner surface walls of the tubular member will effect a transfer of heat into the surrounding fluid, and much of the heat contained within the tubular member which might otherwise be conducted into the fluid will never come into contact with the inner surface walls due to the large amount of wasted spaced within the member. As such, those concerned with the development of immersible heaters have long recognized the need for designing a more efficient means of transferring the heat from a heating element within a tubular member to a surrounding fluid.
The problem of efficient heat transfer from an immersible heater to a surrounding fluid is particularly acute with regard to diesel fuel containers. In this regard, diesel fuel tends to gel in cold climates and as such, there exists a real need for the use of immersible heaters. However, a problem of safety exists in that it is desirable that a very closely controlled heating of the diesel fuel be provided, since excessive heating may result in a combustion of the fuel. It can be appreciated that the Mason heater, as above described, could not efficiently be used as a diesel fuel heater since a controlled heating of the diesel fuel is not possible. This is true due to the fact that the interior of the Mason heater is not designed to selectively circulate heated air in a manner which would permit an operator to accurately estimate the amount of heat being conducted from the heater into the diesel fuel.